Referring to FIG. 1, rail joints comprise of the two rails (1) connected together by a pair of joint (splice) bars (2) and a set of nuts (3) and bolts (4). Together they form the assembly shown in FIG. 1. Since their invention, rail joints have been a weakness in the railway track system. The joint is weaker than the rail section because the bending strength reflected by the section modulus of the two joint bars used at a joint is only a fraction (between twenty percent (20%) and fifty percent (50%)) of the section modulus of the rail section. The weaker joint section causes poor load distribution to the ties, excessive deflection of the rail and pumping of the track. To address this problem, railways worldwide adopted continuously welded rails, which in turn have their own set of problems. Unfortunately, we still need some joints in our system in order to separate the track into signal blocks. The signal bocks allow the train dispatcher to locate trains along the track. The signal blocks are also used for switching of the trains from one track to another and for rail break detection. For each signal block to work efficiently, the rails at adjacent blocks must be electrically isolated from one another.
Along came insulated joints (IJs) such as shown in FIG. 2. These joints have insulating materials (5) between the joint bars (6) and the rail (1) and between the bolts (4) and the rail (1) to ensure that, the two rails at the joint are electrically isolated from one another. Unfortunately, the insulator (5) is the Achilles heel of the IJ system. The polymer material cannot stand the contact and bending stresses from the passage of the train wheels. The problem is worsened by thermal stresses that arise from temperature swings. If the insulating material (5) is made from soft polymer such as rubber, it will cause the joint to flex excessively, loosen the bolts. The polymer will also ooze out at high temperatures. If the polymer is hard enough to maintain its molecular structure at high temperatures, it will be brittle in the winter months and unzip by brittle shear cracking. In either case, the strength of the joint and the excess displacement due to its geometry are not addressed.
In recent times, railways worldwide are pushing for Positive Train Control (PTC) systems that utilize Geo Positioning Satellites (GPS) to move trains. This will reduce the number of locomotive engineers required to operate a train. To ensure that switches are positively locked and lined up with the mainline requires that sturdier and better IJs be designed. Introduction of PTC in a dark territory will necessitate the use of IJs at all switches along the line for the same reason. This salient issue might surface in a few years reinforcing the fact that IJs are here to stay at least for the near term.